This disclosure relates to a mechanism to control the position of a scraper chain conveyor and for detection and adjustment of the tension of a scraper chain of a chain conveyor.
Conveyors, such as armored face conveyors, are part of an integrated longwall system that also comprises a coal-cutting machine and roof supports. As the longwall system removes mineral from the mineral block one strip (web) at a time, the load on the conveyor changes as the cutter moves along the conveyor. The conveyor progressively moves forward one web in order to reposition itself for the next cut.
The mineral being mined is dragged along a top race of the conveyor by a continuous chain and flight-bar assembly driven by sprockets at each end of the conveyor. More particularly, spaced apart chains, with the flight bars connecting the chains, are typical. At the delivery end, the mineral is discharged onto an adjacent conveyor while the continuous chain enters a bottom race where it proceeds to a return end, where a return end drum or sprocket reverses the direction of the chain.
Armored face conveyors normally operate at a fixed overall length (sprocket centers), but more usually they are fitted with an extendable return end frame. The purpose of the extendable return end frame is to take-up slack chain generated during normal operations. The variations in load and the repositioning of the many parts of the conveying system result in changes in chain tensions. To ensure slack chain is not produced, the movement of the extendable return end frame is sometimes automatically controlled to maintain a fixed chain tension.
This repeated action involves the repositioning of the many parts that make-up the total conveying system. Keeping the equipment inline with the coal block is difficult, as no direct steering mechanism is available with these systems. The operators have to rely on their experience by adjusting the relative position of the conveyor to the coal block to counteract a tendency of the equipment to gradually creep sideways. This inevitably results in face creep with the only corrective action available to the operators being to angle the conveyor a few degrees off square to the coal block. This is very slow and extremely difficult to gauge.
In certain operational situations, one of the two chains of the chain and flight bar assembly may get broken on the top race. The remaining chain can then enter the return race with the broken chain. Lower tensions in the bottom race can be contained by the single chain, which continues to the return end and then over the return end sprocket. If the broken chain is not identified on the top race, the result will be failure of the second chain, which is most likely when it approaches the discharge area. Consequence damage to related equipment can then occur. Failure is followed by prolonged down time to make a repair. Visual identification of the broken chain is possible, but is unlikely because the chain is covered with the mineral being conveyed. Additionally, on most installations, safety requirements prohibit operators from being adjacent the return end of the conveyor, which further reduces the opportunity for manual detection.
FIG. 1, which is taken from Bandy U.S. Pat. No. 5,131,528, illustrates a prior art scraper chain conveyor. FIG. 1 illustrates in simple form the various conveyor elements necessary for understanding of the conveyor equipment environment. The conveyor apparatus or assembly is shown generally by the character numeral 10 and includes a drive drum/sprocket 12 and an idler or guide drum/sprocket 14 separated by a span of a flexible conveyor 16, illustrated partially in dashed line outline. As depicted, the conveyor 16 comprises dual conveyor chains 18 and a multiplicity of spaced flight bars 20 attached to the dual chains 18. During operation of the conveyor assembly, the flight bars 20 push aggregate material, such as mined coal, along an underlying conveyor pan 21. The conveyor assembly 10 is typically positioned juxtaposed to a mine wall where a seam of material is being mined for transporting the material to one end. The material is then transferred to an auxiliary conveyor for further disposition.
The drum/sprocket 12 is appropriately coupled to a conveyor drive motor 22. Operation of motor 22 causes the sprocket intermeshing with the dual chains 18 to advance the conveyor 16. A pair of sidewalls 24 forming a first portion of a “split frame” of conveyor assembly 10 serves to rotatably support the drum/sprocket 12. The sidewalls 24 are illustrated as being telescopingly engaged with a second pair of sidewalls 26 forming a second portion of the frame and, collectively with sidewalls 24, comprise the aforementioned split frame. The telescoping joint, indicated generally by character numeral 48, permits the frame portions to be moved relative to one another.
The idler drum/sprocket 14 is appropriately mounted for rotary movement between sidewalls 26. Relative movement at the joint 48 between the adjacent sidewalls 24 and 26 thus causes the distance span between the drum/sprockets 12 and 14 to vary accordingly. The dual conveyor chains 18 can be provided with increased or reduced tension depending upon the direction of adjusting movement of the supporting drum/sprockets with respect to each other. To provide this relative movement, assembly 10 has a tensioning means in the form of a pair of hydraulic cylinders 28 and 30, each mounted on and secured to an adjacent sidewall 26. In other embodiments (not shown), only a single hydraulic cylinder can be used. The cylinders have respective pistons 32 and 34, each of which is operatively coupled to a sidewall 24 in any known and expedient manner.
Movement of the pistons 32 and 34 causes the first portion of the conveyor 16 represented by the side walls 24 to move longitudinally relative to the second portion and side walls 26, thus relaxing or tensioning the chain 18, as desired. Control of movement of pistons 32 and 34 is affected by a conventional hydraulic tensioning control circuitry, depicted generally by numeral 40 in FIG. 1.
As stated above, a certain amount of tensioning of conveyor chain 18 is essential for the proper and efficient operation of the conveyor assembly 10. Too little tension may cause the conveyor chain to ride up the teeth of the sprockets, and even eventually, under severe conditions, become disengaged. Conversely, too much tension may cause the conveyor components to be over stressed, increasing the risk of mechanical failure in the various parts of the conveyor apparatus.
FIG. 2, which is taken from Weigel et al U.S. Pat. No. 7,117,989, illustrates a prior art mechanism for controlling the tension in a scraper chain in a conveyor. FIG. 2 shows a tensionable return station, marked as 51, which forms the auxiliary drive of a face conveyor, and on which a spoked chain wheel 52 is located, which may be powered by drives (not shown).
All channel sections 70 and machine frame 51 and, where applicable, any intermediate or transitional channels located between them, have a top race 54 A and a bottom race 54 B. In top race 54 A the material to be conveyed, such as coal, is transported by means of scrapers 20 as far as the main drive, and in bottom race 54 B the scrapers run back to the auxiliary drive. The constantly changing load conditions in the top race cause the tension in the top race and bottom race sections of conveyor 16 to vary.
In order to detect the tension of conveyor 16, a sensor, indicated overall by 60, is located on the frame of return station 51, which forms the auxiliary drive. The sensor has a sliding body or sensor body 62 with a curved sliding surface 61, which is coupled with a shaft 63 such that it cannot be turned, said shaft reaching obliquely over the conveying trough and return trough for scraper conveyor 16 in top race 54 A of machine frame 51 of the chain conveyor. Shaft 63 is supported in bearing blocks 64, one of which is indicated schematically at the rear side face of return station 51. The weight of sensor body 62 causes its sliding surface 61 to be directly in contact with the upper face of a scraper 20 or with the upper face of vertical chain links 57 in the area of the measuring zone. At the same time, shaft 63, supported in bearing blocks 64 such that it can swivel, forms a measuring shaft, and by means of shaft encoder 65 the relative position of measuring shaft 63 and thus also the relative position or swiveled position of sensor body 62 rigidly coupled with it may be detected and transmitted to the evaluation and control unit 72 via signal line 71. Depending on the measurement signal of shaft encoder 65, evaluation and control unit 72 then activates tensioning drive 55 of return station 51 via signal line 75.
In an extensive zone within top race 54 A of return station 51, referred to below as the measurement zone, and extending between points 67 and 68 in the drawing marked with double arrows, scraper conveyor 16 has vertical play. In other words, between point 67 and point 68 along the track in top race 54 A, conveyor 16 can essentially move freely in a vertical direction, i.e. perpendicularly to the bottom of top race 73, 74.
In the embodiment shown, the scraper chain is running with optimum tension, i.e. some chain links in the measuring zone are slightly lifted away from the bottom of top race 74. When the chain is dangling, on the other hand, chain links 57, 58 and scrapers 59 within the area of the measuring zone and in the area of the machine frame are in contact at every point with the bottom of top race 73 or 74 of return station 51, and sensor body 62 is at its largest downwards deflection. This state is detected by evaluation and control device 72 and tensioning drive 55 is extended. If the tension of scraper conveyor 16 increases, vertical and horizontal chain links 57, 58 together with scrapers 59 of scraper conveyor 16 may move even higher in the measuring zone, due to the absence of restrictive guidance and the existing vertical play (67 or 68), which causes sensor body 62 to be swiveled clockwise and this deflection to be detected by shaft encoder 65 and transmitted to evaluation and control device 72 as a measurement signal. If the chain reaches a preset tension corresponding to that of a tight chain, this is detected directly by shaft encoder 65 as a result of the greater deflection of sensor body 62, and evaluation and control device 72 then activates tensioning drive 55, in some cases via a closed-loop control algorithm, through signal line 75 such that tensioning cylinder 56 is retracted in order to reduce the tension in scraper conveyor 16.
Other mechanisms for monitoring chain tension include U.S. Pat. Nos. 5,505,293, and 4,657,131.